Automatic weld tracer with lateral electrode positioning for lap joints



Sept. 15, 1970 N- J. FERRIER 3,529,125 AUTOMATIC WELD TRACER WITHLATERAL ELECTRODE POSITIONING FOR LAP JOINTS Filed Jan. 24, 1969 SERVO ICY G CONTROLS )0 2" F-l! MA- 7 L &// //s,f

5 7 j] Z Z? zz I NICHOLAS J. FERRIER Attorneys United States Patent US.Cl. 219-125 7 Claims ABSTRACT OF THE DISCLOSURE This disclosure includesa Weld head driven along a weld lap joint of two overlapping plates. Afloating probe unit has a first follower riding on the top of the firstplate and is mounted for linear movement normal to the weld joint andfor pivotal vertical movement. A pair of linear voltage differentialtransformers are mounted to the probe unit and the cores positioned inaccordance with the weld joint. The output of the transformers locatesthe tip of a consumable electrode on the center of the top edge of thefirst plate. A lateral positioning follower is connected to the firstfollower and extends downwardly into engagement with the face of thefirst plate and positively prevents the first follower from moving inbeyond the center of the plate. The electrode is thereby properlycentered on the edge and prevented from missing the edge of the outerplate at a gap between the two plates.

This invention relates to a tool control tracer apparatus andparticularly to locating a welding electrode in a lap joint for welding.

In arc welding and the like, automatic apparatus is often required tofollow a contoured weld seam which may move in any one of a plurality ofdirections. Various systems have been suggested for controlling themovement of a weld electrode in accordance with the changing contour ofa weld seam. The application of Bollinger et al. entitled AutomaticTracer for Positioning Control which was filed on the same date as thisapplication and is assigned to the same assignee discloses a reliableand practical probe follower system for accurate positioning of awelding head and electrode. Generally, as disclosed in that application,the Welding apparatus with the electrode is driven with a givenhorizontal speed. A probe follower rides on the upper edge of a lapjoint and is urged into sliding engagement with the face of the adjacentweld member. The probe follower senses any vertical or horizontaldisplacement of the seam and provides respective voltages proportionalthereto. The voltages are interconnected to directly drive servo motors,to reposition the weld nozzle and therefore the electrode in thecorresponding directions. In addition, the weld nozzle may be tiltedabout a horizontal axis and about a vertical axis. Such a five axiscoordinate system has been found to provide a highly desirable and veryreliable welding apparatus for moving of a welding assembly in a pair ofplanes while maintaining the electrode in a predetermined desiredposition with respect to the depositing of the weld metal.

Such an apparatus has provided highly satisfactory welds. Where theparts to be welded are overlapped platelike members defining a lapjoint, however, the weld metal does not bridge gaps in the joint whichare caused by deformation such as flower potting of the outer platelikemember defining the edge upon which the follower rests. Applicantdiscovered that the defects arose because the follower moves into thegap and thus generates a corrective signal as if the edge had dropped,even though it has not. The corrective signal of course correspond-3,529,125v Patented Sept. 15, 1970 ingly repositions the weld electrodesuch that it moves onto the inner plate-like member and the gap at theedge is not bridged with a resultant defective weld at that point.

The present invention is particularly directed to a floating type probemeans having a double follower which accurately tracks and producesoutput signals to maintain the electrode in position to bridge suchgaps.

The probe follower in accordance with invention includes a first membersuch as a pencil-like rod which rides on the top edge of the seamdefined by a pair of overlapping plates. A second member is fixed to thefirst member and extends downwardly into engagement with the outer faceof the adjacent plate. The probe follower is connected in the controlcircuit to position the electrode in both the vertical and thehorizontal direction. The second member establishes a reference tolocate the elec trode with respect to the top edge of the outer plate,preferably midway, and insure that the electrode is properly located tobridge minor gaps at the joint.

The drawing furnished herewith illustrates the best mode presentlycontemplated by the inventor for carrying out the subject invention anddisclose the above advantages and features as well as others which willbe readily understood from the following description.

In the drawing:

FIG. 1 is an elevational view of a welding assembly constructed inaccordance with the present invention;

FIG. 2 is an enlarged side elevational view of the probe follower unitshown in FIG. 1;

FIG. 3 is a simplified vertical section showing the movement of thefollower unit shown in FIG. 2; and

FIG. 4 is a diagrammatic top View of FIG. 3.

Referring to the drawings and particularly to FIG. 1, the presentinvention is illustrated in connection with an automatic arc weldingapparatus including a supporting frame structure 1 within which a pairof overlapping metal plates 2 and 3 are disposed and secured in fixedrelationship by a clamp structure 4. The overlapping metal plates 2 and3 are clamped in a vertical position to define a weld lap joint seam 5at the position of overlap which is to be provided with a continuousinterconnecting weld 5a. In the illustrated embodiment of the invention,an arc welding head 6 is movably supported within the supporting framestructure 1 to follow the weld seam 5 and to direct a weld electrode 7toward the seam and by applying a welding potential between theelectrode 7 and the plates 2 and 3 establishing a welding arc whichcontinuously deposits electrode metal onto the seam 5. The weld head 6and in particular the tip of the weld electrode 7 may be provided withsuitable controls for positioning along the three coordinated axes ofthe Cartesian coordinate system as well as angularly oriented about twoof the axes.

The overlapping plates 2 and 3 are secured within the structure 1 withthe seam 5 extending generally in a horizontal plane which ishereinafter defined or related to the X-coordinate axis direction of theCartesian coordinate system.

Generally, the suporting structure 1 includes a vertical column 8 withinwhich a vertical positioning square shaft of the vertical shaft 9 whichdefines the Y-way control or support for the weld head apparatus. Thecolumn 8 in addition is mounted by a Z-way carriage or support 10 whichin turn is movable along an X-way support 11 to allow movement of thetotal assembly on the three coordinate axes with respect to the weldseam 5.

The column 8 is driven along the X-way by an X-axis drive motor 12 asshown in FIG. 1. The Y-axis drive motor 13 is mounted to the top of thecolumn 8 and coupled to the vertical shaft 9 for positioning of the weldhead 6 in the Y-direction. A Z-axis drive motor 14 is coupled to thecolumn 8 through a suitable screw drive or the like for positioning ofthe column 8 and therefore the weld head 6 in the Z-axis direction alongthe support 10. In addition to the three coordinate drives, the weldhead 6 and attached electrode 7 are adapted to be positioned about afirst angle in the X-Y or vertical plane and a second angle in the XZplane by a suitable means such as referred to in the co-pendingapplication of J. D. Bollinger et al.

The present invention is particularly directed to the controlledactuation of the Z-axis motor 14 in accordance with the output of atransducer 15 which includes a probe tip 16 following the seam 5.

More particularly, in the illustrated embodiment of the invention, anL-shaped mounting frame 17 is secured to the lower end of the shaft 9.The L-shaped mounting frame 17 extends laterally outwardly from the workwith a depending leg extending downwardly and terminating in asupporting base or plate 18. The transducer 15 and the arc welding head6 are secured to the mounting plate 18. Head 6 includes weld nozzle 19through which the electrode 7 is fed to the seam 5. The nozzle 19 andtransducer 15 are connected to and supported by a common support shaft20 for a corresponding orientation with respect to seam 5.

Transducer 15 is connected to an L-shaped bracket 20a secured to the endof shaft 20 and mounted as more fully disclosed in the previouslyreferred to Bollinger et al. application.

Referring particularly to FIG. 2, the transducer 15 includes a probebody portion 21 to which the probe tip 16 is attached. The probe bodyportion 21 is shown as a rectangular block of a suitable lightweightmetal such as copper which is slidably mounted within a generallyrectangular supporting frame or housing 22.

A cantilivered spring member in the form of a fiat leaf spring 23secures the rearward or outermost end of the body portion 21 to housing22.

The forward end of the body portion 21 is supported by a pair of springmeans 24 and 25 interconnected respectively to the top and bottomsurfaces of the probe means and the adjacent housing. Each of thesprings 24 and 25 is a similar spring metal band bent into a loop springof a generally rectangular shape. The loop type construction permits therectilinear movement of the probe body portion 21 in the horizontalplane while also permitting the vertical pivotal movement of the bodyportion 21 with the pivot point being defined by the cantilevered spring23 and its attachment to the body portion 21. The rectilinear motion andthe pivotal motion of the body portion 21 are similarly individuallydetected by a pair of linear voltage differential transformers 26 and 27mounted to the top and side of the transducer 15. The transformers 26and 27 are similarly constructed in accordance with well-knownconstruction includes a fixed winding, not shown, to which suitableelectrical inputoutput leads are connected. The output is controlled bythe actual positioning of a core of which only the core 28 for thetransformer 27 is shown for purposes of clearly disclosing the controlalong the Z-axis or direction.

A lightweight arm 29 is secured to the sidewall of the body portion 21along the axis of movement and projects outwardly in front of the core28 such that the core is positioned in accordance with the position ofthe probe unit 16 in the Z-direction.

The first plate 2 may not always follow precisely the immediate face ofthe first plate 2 as a result of manufacturing tolerances and the like.The plate 2 may therefore define a gap 30 in the Z-direction, as shownin FIGS. 3 and 4. If a single follower 31 rides on the seam top edge 32,as shown in phantom in FIGS. 3 and 4, encounters an opening or gap 31,it would tend to move into the gap 30 to vary the Y-axis positioning butmaintain the Z-axis positioning in the coordinate servo system. This hasbeen found to result in a locating of the electrode tip into the gap 30with the weld metal deposited essentially on the inner rail or plate 2without bridging the gap.

The present invention is particularly directed to positioning of core 28in accordance with the rectilinear movement of the probe body portion 21in the Z-direction to generate a corresponding output signal which isemployed to reposition the weld head 6 and particularly the electrode 7with respect to the weld seam 5.

The probe tip 16 in accordance with the present invention includes apair of followers 33 and 34 riding respectively upon the top edge 32 andthe adjacent outer face 35 of the outer plate 2.

In the illustrated embodiment of the invention, the probe tip 16includes a generally curved mounting arm 36, the inner end of which isclamped or bolted to the body portion 21, as at 37. The mounting arm 36curves upwardly and laterally toward the weld seam 5 with the outer endof the arm disposed somewhat above the weld seam 5.

The first follower 33 is a pointed pencil-like member which is welded,threaded or otherwise secured to the outermost end of the arm 36 andextends angularly downwardly toward the seam 5 with the outermost endterminating in a wear-resistant end riding on the upper edge 32 of thefirst outer plate 2. The follower 33 engages the plate 2 in alignmentwith the extension of the axis of the body portion 21 in the Xcoordinate direction and in the X-Z plane through the axis.

The second follower 34 is secured to arm 36 and extends downwardly belowthe level of the top edge 32 and terminates in sliding engagement withthe outer faces of the first plate 2. The tip of the follower 34 engagesthe adjacent surface in alignment with the tip of follower 33, as shownin FIG. 4.

The probe tip 16 is preferably formed of copper or other material havingexcellent heat conducting qualities. The probe tip 16 is furthermorepreferably clamped in heat exchange engagement to the body portion 21such that the total probe assembly rapidly dissipates the heat resultingfrom the welding arc.

In the operation of the illustrated embodiment of the invention, theweld head 6 and the attached transducer 15 are aligned with the startingposition of the lap point of the overlapping plates 2 and 3. Theelectrode 7 is energized through a suitable feed system and fed into theseam 5. Simultaneously, the X-axis drive motor is energized to move thetotal assembly along the weld seam 5 in the X-direction. The transducer15 and particularly the probe followers 33 and 34 sense the movement ofseam 5 in the Y-direction and in the Z-direction and provides thenecessary signals for optimum positioning of the weld head 6 andattached electrode 7 in both the Y-direction and Z-direction.

The Z-direction is particularly controlled by the lateral position ofthe outer weld plate 2. If the plate 2 moves outwardly in theZ-direction or away from the weld head 6, the probe follower 34 movesoutwardly under the action of the cantilever spring 23 and the forwardsprings 24 and 25. This, in turn, repositions the core 28 of thedifferential transformer 27 and generates an electrical signal which isimmediately transmitted back to the servo system for the Z-axis drivemotor 14 and causes it to move the column 8 to which the weld head 6 andtransducer 15 are interconnected in the Z-direction to reposition theelectrode tip 7. This movement does not effect any of the othercomponent directions and in particular the other differentialtransformer 26.

If the weld plate 2 should be deformed inwardly with a resultant gap 30,the follower 34 is forced inwardly toward head 6 against the forces ofsprings 23, 24 and 25 to generate a corresponding repositioning signalsuch that the Z-axis drive motor 14 is energized to center the electrode7 on the top edge. The electrode 7 is therefore maintained centered onthe top edge 32 to produce a continuous weld joint a connecting the workmembers or plates 2 and 3.

The present invention provides a floating type support for the tracerwhich creates an optimum location of the electrode with respect to thetop edge of a lap joint for insuring a continuous weld joint.

Iclaim:

1. A weld tracer apparatus for positioning a welding electrode withrespect to a pair of overlapping and abutting plate-like metal membersdefining a Weld seam at the edge of the first metal member, comprising afollower element positioned to ride against the face of the first metalmember immediately below said edge, a second follower element positionedto ride on the edge, and signal means coupled to the follower elementsto sense the lateral displacement of the edge by the first namedfollower element and generate a proportional correction signal forlaterally positioning of the electrode and to sense the displacement ofthe edge by the second named follower element and generate aproportional signal for parallel positioning of the electrode.

2. The weld tracer apparatus of claim 1 wherein said second followerelement is connected to said first follower element, and said signalmeans include first and second signal means coupled to sense ahemovement of only the corresponding follower element.

3. The tracer apparatus of claim 2 wherein said signal means includes apair of differential transformer means mounted to respond to thecorresponding movements of the follower elements in accordance with therespectively engaged surfaces.

4. The weld tracer apparatus of claim 2 having both follower elementsconnected to a body portion, spring means secured to said body portionand including a pivot support means and a linear support meansconjointly supporting the body portion with said pivot support meansaccommodating movement of the body in the plane of movement of thesecond element and said linear support means accommodating movement inthe plane of movement of the first element.

5. The weld tracer apparatus of claim 2 wherein said second followerelement includes a tip adapted to ride on said edge and said firstfollower element is spaced in accordance with a preselected proportionof the thickness of the first member to slidably engage the face of theadjacent plate-like member and to locate the first follower elementcentrally of the edge and in spaced relation to the second plate-likemember.

6. A weld tracer apparatus for positioning a welding electrode withrespect to a pair of overlapping and abutting plate-like metal membersdefining a weld seam between the edge of the first metal member and theadjacent face of the abutting second metal member, comprising firstsensor means connected to the electrode and positioned to ride againstthe face of the first member to sense the lateral position of the edgeof the first metal member relative to said second metal member, controlmeans responsive to said first sensor means to generate an electricalcontrol signal and maintain the welding electrode in predeterminedoverlying lateral alignment to the edge of the first metal member, andsecond sensor means to detect the contour of the edge and having signalmeans to correspondingly position the electrode With respect to thecontour of the edge.

7. The tracer apparatus of claim 6 wherein said control means maintainssaid electrode located essentially centrally of said edge.

References Cited UNITED STATES PATENTS 2,288,032 6/1942 Smith 219-1252,395,525 2/1946 Wilkie et al. -62 2,827,548 3/1958 Griswold 219-2,839,663 6/1958 McCollom 219-76 3,084,246 4/1963 Rieppel et al. 219-137X 3,122,970 3/1964 Rhoades 336-30 X 3,171,012 2/1965 Morehead 219-1243,199,056 8/1965 Cameron 336-30 X 3,281,047 10/1966 Weicht 219-125 XJOSEPH V. TRUHE, Primary Examiner L. A. SCHUTZMAN, Assistant ExaminerU.S. Cl. X.R. 90-62; 228-8

